1. Field of the Invention
The present invention relates to laboratory refrigeration units designed for refrigerating and freezing laboratory samples. More particularly, the invention relates to a programmable electronic start-up delay for delaying the start-up of refrigeration units after a power failure for a user-programmable variable delay period so that a group of refrigeration units can be restarted at different time intervals.
2. Description of the Prior Art
Laboratory refrigeration units such as ultra low temperature freezers are used to freeze or refrigerate laboratory samples such as tissue, blood and plasma. Laboratory samples are often held in these types of refrigeration units for years; therefore, it is critical that the units always remain in operation.
Facilities using a plurality of these types of refrigeration units are subject to potential catastrophic shutdowns during power failures. Specifically, if a plurality of refrigeration units all connected to the same power circuit attempt to restart after a power failure, the power circuit will likely be overloaded and will trip a breaker or fuse and/or fail entirely. This would result in a long-term shutdown of the refrigeration units, causing the laboratory samples contained therein to be damaged.
It is known to delay the start-up of a group of refrigeration units with solid-state delay devices placed in the circuit supplying power to the units. These prior art delay devices are not entirely satisfactory, however, because they are costly, difficult to install, and take up valuable space. Moreover, it is difficult or impossible to modify the start-up delay time period of these prior art devices after they are installed.